A method for reducing axial temperature differences in a steel coil annealing process using a liner

Abstract

The application discloses a method for reducing axial temperature difference in a steel coil annealing process by using a gasket, belongs to the technical field of metal heat treatment processes and equipment, and meets the green manufacturing category, and comprises the following steps: covering a high-temperature-resistant alloy woven mesh on a flexible porous medium made of aluminum silicate fibers to manufacture a modular flexible heat insulation core gasket; secondly, the core gasket is assembled in an upper region of a protective cover to construct a local heat resistance buffer zone, and a non-continuous stress release connecting structure is used to connect inner and outer metal boundaries; finally, in an annealing core heating interval, the buffer zone is used to block the upper strong heat radiation, and the sliding gap of the connecting structure is used to absorb the differential thermal expansion displacement of the inner and outer components. The application effectively solves the problems of thermal stress tearing and heat insulation material fluid scouring failure caused by traditional full-welding connection, significantly suppresses the axial temperature gradient of the steel coil, and improves the annealing quality.

Description

Technical Field

[0001] This invention relates to the technical field of metal heat treatment process and equipment, which falls within the scope of green manufacturing, and particularly to a method for reducing axial temperature difference during steel coil annealing using a gasket. Background Technology

[0002] In the annealing process of cold-rolled steel coils, annealing is necessary to ensure the coil's performance. A certain amount of protective gas is introduced to remove impurities and improve the coil's properties. The coil is placed on a smooth metal base to prevent additional negative impacts during heating. The furnace is enclosed by a heat-resistant stainless steel protective cover, through which protective gas is introduced. Heat originates from high-speed jet burners arranged along the furnace wall. The high-temperature thermal radiation generated by the burners first heats the protective cover, which then transfers heat to the coil inside through convection and radiation. During this process, due to the decreasing density of the hot gas, it naturally rises, creating a significant temperature stratification along the height of the protective cover, with the upper part significantly warmer than the lower part. The upper surface of the coil receives a much greater heat flow than the lower surface, resulting in a non-negligible temperature gradient along the coil's axial direction. Since the coil itself is a tightly wound cylinder of multiple layers of metal strip, its radial thermal conductivity is limited, and the axial temperature difference is further manifested as differences in expansion between the outer and inner rings, and between the upper and lower ends. Uneven thermal expansion can induce large tangential stress between the layers of the strip. When the stress exceeds the yield strength of the material at that temperature, micro-displacement and plastic deformation will occur between the layers, eventually forming defects such as strip indentations on the surface of the strip.

[0003] In existing technologies, to mitigate the axial temperature difference of steel coils under rapid heating conditions, a metal lining is welded to the outside of the protective cover, and static refractory cotton is filled between the lining and the protective cover to form a heat insulation structure. However, the above solution has revealed two types of failure problems in industrial applications: such as Figure 2 As shown, thermal shock failure occurs at the mechanical structural level. The metal liner and the protective cover are fixed using continuous full welding. During the intense alternating hot and cold cycles from room temperature to high temperature, the inconsistent thermal expansion of the two components, coupled with rigid constraints, prevents the expansion displacement from being released, generating high-amplitude shear stress. This causes the liner to bulge and eventually tear the weld. At the material level, hydrodynamic failure occurs. After weld cracking or poor end sealing, the high-speed circulating protective gas in the annealing furnace directly enters the insulation layer. The exposed refractory fibers rapidly oxidize, become brittle, and pulverize under the combined scouring of high temperature and airflow, resulting in complete loss of insulation function within several production cycles. The detached fiber debris also contaminates the steel coil surface, causing additional quality problems. These defects make it difficult for the insulation device to operate long-term under the conditions of a rapid annealing unit, increasing energy and material costs, resulting in a high scrap rate and resource waste. To align with the concept of green manufacturing, this invention proposes a method using a gasket to reduce the axial temperature difference during steel coil annealing to solve these problems. Summary of the Invention

[0004] This invention overcomes the shortcomings of the prior art and provides a method for reducing axial temperature difference during the annealing process of steel coils by using a gasket.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for reducing axial temperature difference during steel coil annealing using a gasket, comprising: S1. High-temperature resistant physical coating and isolation are applied to flexible porous media to create modular flexible heat insulation core pads; S2. The flexible heat insulation core pad is assembled on the upper middle part of the outer side of the inner protective cover body to withstand heat radiation, forming a local heat barrier buffer zone. A discontinuous stress relief connection structure is constructed between the inner protective cover body and the outer metal liner of the local heat barrier buffer zone. The inner protective cover body and the outer metal liner together constitute the metal protective cover. S3. Annealing and heating the metal protective cover equipped with a local thermal barrier buffer zone and the cold-rolled steel coil inside it. When the ambient temperature inside the furnace enters the core heating range, the local thermal barrier buffer zone is used to block the direct thermal radiation from the heat source of the annealing furnace to the upper part of the inner protective cover body, thereby reducing the difference in thermal conduction rate between the two ends of the cold-rolled steel coil in the axial direction. S4. During the high-temperature annealing process, a discontinuous stress-relieving connection structure is used to absorb the differential thermal expansion displacement between the inner protective cover body and the outer metal liner caused by temperature changes, so as to complete the annealing process. The modular flexible heat insulation core pad is a liner used to reduce the axial temperature difference during the annealing process of steel coils. The liner is composed of a flexible porous medium that is physically coated and isolated by high temperature resistance, and forms the local heat barrier buffer zone by being assembled on the upper middle part of the outer side of the inner protective cover body to withstand heat radiation.

[0006] In a preferred embodiment of the present invention, in step S2, the discontinuous stress relief connection structure uses discretely arranged metal bridging blocks as the transition connection medium between the inner and outer boundaries. One end of the metal bridging block is rigidly fixed to the inner protective cover body, and the other end is connected to the outer metal liner by a guide groove with sliding clearance, allowing the outer metal liner to slide freely along the axial direction to release thermal expansion potential energy.

[0007] In a preferred embodiment of the present invention, in step S2, the local thermal barrier buffer strip is only assembled in the upper part of the inner protective cover body. The upper part of the inner protective cover body is defined as the horizontal cross-section extending upward from the bottom load-bearing flange of the inner protective cover body at a distance of 1500mm~1800mm to the top arc-shaped dome area of ​​the inner protective cover body. It is used to target and weaken the thermal radiation in this area and compensate for the uneven distribution of heat in the furnace. The local thermal barrier buffer strip is formed by the flexible heat insulation core pad as a liner.

[0008] In a preferred embodiment of the present invention, in step S1, the high-temperature resistant physical coating and isolation uses a high-temperature resistant alloy woven mesh to wrap the flexible porous medium. The seams of the wrapping are made using a folded edge-wrapping process with an overlap width of 20mm~30mm. After wrapping, the medium is mechanically sewn with metal wire of the same material as the high-temperature resistant alloy woven mesh, and the stitch spacing is controlled at 10mm~15mm. The flexible porous medium wrapped by the high-temperature resistant alloy woven mesh constitutes the heat insulation body of the pad.

[0009] In a preferred embodiment of the present invention, in step S2, a flow-blocking baffle is added inside the connection gap of the discontinuous stress relief connection structure. The root of the flow-blocking baffle is fixed to the outer wall of the inner protective cover body. The baffle blocking surface is perpendicular to the airflow direction and a dynamic clearance gap is reserved between it and the inner wall of the outer metal liner to cut off the direct scouring path of the high-speed protective gas on the flexible heat insulation core pad.

[0010] In a preferred embodiment of the present invention, in step S1, the flexible porous medium is selected from aluminum silicate fiber, and the bulk density is controlled at 96 kg / m³. 3 ~128kg / m 3 The thickness is controlled between 40mm and 60mm to establish a gentle temperature gradient attenuation zone in the target area.

[0011] In a preferred embodiment of the present invention, in step S2, a radial assembly interference is applied during the assembly of the flexible heat insulation core pad. The radial geometric gap between the inner protective cover body and the outer metal liner is smaller than the initial natural thickness of the flexible heat insulation core pad, so that the flexible heat insulation core pad is forcibly compressed to form a continuous elastic restoring force to tightly fit the inner and outer metal surfaces. The flexible heat insulation core pad is pressed between the inner protective cover body and the outer metal liner as a pad.

[0012] In a preferred embodiment of the present invention, in step S3, the core heating range refers to the temperature range in which the furnace ambient temperature rises from 400°C to 1000°C. Within this range, heat transfer in the annealing furnace is dominated by thermal radiation. The comprehensive heat transfer coefficient of the upper region of the inner protective cover body is reduced by the local thermal barrier buffer zone, which suppresses the heat conduction rate of the upper end face of the cold-rolled steel coil, provides a time window for heat accumulation on the lower end face, and smooths out the axial temperature gradient inside the cold-rolled steel coil.

[0013] In a preferred embodiment of the present invention, in step S1, after the flexible porous medium is cut, a uniform pre-stress of 0.05MPa to 0.1MPa is applied, and then a high-temperature resistant physical coating is applied for isolation.

[0014] In a preferred embodiment of the present invention, the outer metal liner is made of 310S austenitic heat-resistant alloy stainless steel with a thickness of 3mm to 5mm, wherein the liner is composed of a flexible porous medium that has been pre-stressed and then physically coated and isolated at high temperatures.

[0015] This invention addresses the shortcomings of the prior art and has the following beneficial effects: (1) This invention constructs a local thermal barrier buffer zone on the external thermal radiation path of the metal protective cover, and uses the low thermal conductivity of the flexible heat insulation core pad to forcibly weaken the direct thermal radiation intensity of the upper space of the annealing furnace to the upper part of the steel coil, thereby smoothing the internal temperature gradient of the steel coil along the axial height direction and eliminating the relative slippage and thermal stress misalignment between the layers of the steel coil caused by the severe mismatch of thermal expansion. Compared with the existing rapid heating process where heat accumulates at the top, resulting in a huge temperature difference between the upper and lower end faces of the steel coil and a high risk of serious surface physical defects, this solution reduces the strip-shaped indentation defects on the surface of the steel coil without sacrificing the overall heating efficiency and production capacity of the rapid annealing unit.

[0016] (2) This invention constructs a discontinuous stress-relieving connection mechanism between the inner and outer boundaries of the local thermal barrier buffer zone. When subjected to severe alternating hot and cold cycles from room temperature to high temperature, the outer boundary is allowed to slide relative to each other within the reserved geometric gap. The differential thermal expansion potential energy generated by uneven heating of the inner and outer boundaries is converted into non-destructive mechanical displacement, effectively relieving and releasing the internal shear stress that attempts to tear the connection. Compared with the existing technology that uses a rigid continuous full welding process to fix the outer liner, which is prone to severe bulging deformation and weld fracture under extreme thermal shock conditions, this solution avoids the structural failure of the protective cover under alternating high temperature environment and maintains the long-term structural integrity of the physical shell.

[0017] (3) This invention creates a modular flexible heat insulation core pad by physically encapsulating and isolating the flexible porous medium with high temperature resistance, and then combining it with a flow-blocking baffle. The dense metal mesh and the baffle structure together form a physical barrier, cutting off the protective atmosphere circulating at high speed in the annealing furnace and the direct hydrodynamic scouring path of the fragile heat insulation medium. At the same time, it gives the loose fiber an overall mechanical support force, preventing the heat insulation material from settling, oxidizing and pulverizing under the dual effects of gravity and thermal shock. Compared with the existing technology that exposes the heat insulation cotton and fills the gaps, once the external weld cracks, it will quickly lose its heat insulation function and generate debris under the scouring of high temperature airflow. This solution ensures the long-term thermal resistance stability of the heat insulation core pad in the harsh industrial environment, and avoids secondary pollution of the surface of high-quality cold-rolled steel strip by pulverized impurities.

[0018] (4) The present invention uses a modular flexible heat insulation core pad as a liner to assemble in the upper middle part of the outer side of the inner protective cover body, and with the help of a discontinuous stress relief connection structure, so that the liner can stably form a local thermal barrier buffer zone in the annealing core heating range, continuously reducing the heat radiation input in the upper part of the protective cover; at the same time, the discontinuous stress relief connection structure can release the differential thermal expansion displacement between the outer metal liner and the inner protective cover body, avoiding the outer metal liner from bulging, cracking or weld tearing due to rigid constraints, thereby maintaining the assembly stability and heat insulation performance of the liner and improving the service reliability of the device in multiple annealing cycles. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is a flowchart of the steps of the method of the present invention; Figure 2 This is a schematic diagram of the structure of a protective cover with a continuous full-welded outer lining structure in the prior art, which shows weld cracking and lining exposure after annealing cycle. Figure 3 This is a schematic diagram of a structure in which a discontinuous connecting member is provided at the crack in one embodiment of the present invention; Figure 4 This is an external structural diagram of the inner cover repaired by the continuous welding method of the present invention, after four rounds of annealing tests, showing obvious deformation at the top; Figure 5 This is an external structural diagram of the inner cover repaired using discontinuous connectors according to the present invention, which showed no obvious deformation after four rounds of annealing tests. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0022] Application Overview: This invention targets the intermittent heat treatment process of steel coils in an annealing unit. Inside the protective cover, under the high-temperature thermal radiation of the jet burner, heat significantly accumulates in the upper part of the cover, with the upper surface of the steel coil consistently receiving a much higher heat flux density than the lower surface. Due to the limited thermal conductivity of the steel coil itself, axial heat conduction cannot adequately compensate for the heating difference between the two ends, resulting in a significant internal temperature gradient. Existing techniques, such as directly fixing an insulating liner to the outside of the protective cover, are limited by the requirement of strong constraint by continuous full welding connecting dissimilar metal components. Under rapid temperature changes, the thermal environment and heating rate of the liner and the protective cover shell differ, leading to a significant difference in their thermal expansion displacement. The rigid welded joint converts all expansion potential energy into internal stress, which, exceeding the material's high-temperature yield limit, results in plastic buckling and weld failure.

[0023] The existing solution fails to effectively address the problem because it neglects the expansion coordination mechanism between the protective cover and additional components under alternating temperature fields. Conventional full-welded connections completely lock the outer liner to the protective cover surface, severely restricting thermal expansion and preventing internal stress release through displacement. This leads to the eventual tearing of any heat-resistant metal interfaces due to accumulated shear stress. Furthermore, the selected fiber-based porous insulation material is directly exposed within the annular cavity and connected to the outside, lacking protection against forced convection. In the forced circulating airflow environment of the annealing furnace, high-speed gas directly erodes the fiber structure. The material's microstructure cannot withstand the combined effects of fluid shear force and high-temperature oxidation, resulting in rapid structural collapse and material loss.

[0024] This invention constructs a local thermal barrier buffer zone and sets up a discontinuous stress-relieving connection mechanism between the inner and outer metal boundaries. It uses intermittent bridging components to connect the inner and outer boundaries and reserves geometric gaps at the connection points to allow for thermal expansion. This allows the outer boundary to expand and contract freely at high temperatures, converting the potential energy of thermal expansion into harmless displacement and avoiding stress concentration at the welded joint. At the same time, the flexible porous medium within the buffer zone is fully encased and isolated by high-temperature resistant metal wire mesh to form a modular core pad. A flow-blocking baffle is added to the inside of the connection gap to cut off the direct hydrodynamic scouring path of the external high-speed protective gas on the fiber material.

[0025] Exemplary method: like Figure 1 As shown, a method for reducing axial temperature difference during steel coil annealing using a gasket includes: S1. High-temperature resistant physical coating and isolation are applied to flexible porous media to create modular flexible heat insulation core pads; S2. The flexible heat insulation core pad is assembled on the upper middle part of the outer side of the inner protective cover body to withstand heat radiation, forming a local heat barrier buffer zone. A discontinuous stress relief connection structure is constructed between the inner protective cover body and the outer metal liner of the local heat barrier buffer zone. The inner protective cover body and the outer metal liner together constitute the metal protective cover. S3. Annealing and heating the metal protective cover equipped with a local thermal barrier buffer zone and the cold-rolled steel coil inside it. When the ambient temperature inside the furnace enters the core heating range, the local thermal barrier buffer zone is used to block the direct thermal radiation from the heat source of the annealing furnace to the upper part of the inner protective cover body, thereby reducing the difference in thermal conduction rate between the two ends of the cold-rolled steel coil in the axial direction. S4. During the high-temperature annealing process, a discontinuous stress-relieving connection structure is used to absorb the differential thermal expansion displacement between the inner protective cover body and the outer metal liner caused by temperature changes, so as to complete the annealing process.

[0026] In this application, the modular flexible thermal insulation core pad is a liner used to reduce the axial temperature difference during the annealing of steel coils. The liner is composed of a flexible porous medium that is physically coated and isolated by high temperature resistance. The flexible porous medium serves as the thermal insulation body of the liner, and the high temperature-resistant physical coating and isolation structure is used to externally constrain and protect the flexible porous medium from erosion, enabling the liner to maintain overall structural stability in the high temperature and protective gas circulation environment of the annealing furnace.

[0027] The challenge in implementing the above technical solution lies in transforming static insulation into an engineering-feasible, long-life physical device within an alternating high-temperature oxidizing environment, and integrating it into existing annealing processes. Considering the complex fluid dynamics, solid mechanics, and thermal radiation coupling field inside the annealing furnace, a macroscopic physical barrier is needed to protect the fragile insulation medium before process execution. A stress-relieving mechanism should be introduced during the assembly stage to ensure that the device can stably mitigate temperature differences during subsequent heating processes, thus enabling industrial-grade continuous production.

[0028] Step S1 is the material basis and physical premise for constructing the subsequent local thermal barrier buffer zone, transforming the microscopically fragile thermal insulation material into a macroscopic structural component that can work stably for a long time in extreme alternating thermodynamic and hydrodynamic environments. In S1, a high-temperature resistant physical coating is applied to the flexible porous medium to create a modular flexible thermal insulation core pad.

[0029] Specifically, flexible porous media refers to composite structural materials containing a large number of microscopic non-directionally arranged solid fiber skeletons with abundant tiny air gaps between the fiber skeletons. The thermal insulation principle of the above materials relies on their extremely high porosity. The interlaced microfibers divide the space inside the material into countless tiny static air chambers. Since the thermal conductivity of static air is extremely low, and the complex fiber network can effectively increase the path length of heat conduction and scatter externally incident thermal radiation photons, it exhibits an extremely low thermal conduction rate on a macroscopic scale.

[0030] In the field of industrial heat treatment, alternative materials for flexible porous media include glass fiber, rock wool fiber, alumina fiber, and aluminosilicate fiber. While glass fiber possesses good flexibility, its softening point is typically below 600℃, and it rapidly melts and collapses at the core operating temperature of annealing furnaces, reaching up to 1000℃, losing all its porous structure. Rock wool fiber, although lower in cost, is highly susceptible to crystallization reactions and severe volume shrinkage at temperatures exceeding 800℃, leading to macroscopic voids in the insulation layer. Alumina fiber, while possessing excellent resistance to ultra-high temperatures, suffers from an extremely brittle microcrystalline structure, making it prone to breakage and pulverization under the periodic mechanical vibrations of the annealing furnace base.

[0031] Based on the specific operating conditions of the annealing process, this invention preferentially uses loose, multi-interval aluminosilicate fibers as the basic material for constructing flexible porous media. Aluminosilicate fibers are melt-spun from alumina and silica, and their phase transition temperature is higher than the maximum operating temperature of the annealing furnace. In a long-term alternating heating environment of 1000℃~1200℃, aluminosilicate fibers can maintain the microscopic stability of their amorphous structure without significant volume shrinkage or grain coarsening. Simultaneously, aluminosilicate fibers possess excellent flexibility and tensile strength, enabling them to withstand repeated thermal expansion and contraction deformation without breaking.

[0032] Heat transfer within flexible porous media consists of three parts: solid-state heat conduction through the fiber skeleton, convective heat conduction of the gas within the pores, and radiative heat conduction through the pores.

[0033] For example, if the fiber bulk density is too low, below 60 kg / m³ 3 If the pore size inside the material is too large, heat radiation under high-temperature conditions can penetrate the medium, leading to overall thermal insulation failure; if the bulk density is too high, for example, above 160 kg / m³, it will also cause thermal insulation failure. 3 Although heat radiation is effectively blocked, the increased density of the fiber skeleton leads to an increase in the heat conduction flux of the solid, while the material loses its flexibility.

[0034] Preferably, the bulk density of the aluminosilicate fiber is 96 kg / m³. 3 ~128kg / m 3 Within this range, the density of the fiber network is just enough to reduce the pore diameter to near the mean free path of gas molecules, thereby maximally restricting the microscopic thermal motion of air molecules within the pores and cutting off convective heat transfer paths. Simultaneously, the moderate mass of the fiber skeleton within this density range minimizes the combined effect of solid-state thermal conductivity and radiative thermal conductivity. Based on the heat flux density distribution within the annealing furnace, the thickness of the flexible porous medium in this invention is 40mm~60mm, which can establish a sufficiently gentle temperature gradient attenuation zone within the target area, weakening the strong thermal radiation outside the protective cover to a level that the cold-rolled steel coil can balance through its own internal heat conduction.

[0035] In existing technologies, directly filling exposed fiber materials into metal gaps presents severe hydrodynamic challenges in actual production. The annealing furnace not only experiences extremely high temperatures but also carries high-speed circulating protective gas with velocities reaching 10-20 m / s. When the furnace temperature changes drastically, uneven thermal expansion of the metal components causes deformation gaps. According to the Bernoulli effect in fluid mechanics, high-speed gas flowing through the gaps creates localized negative pressure or directly forms a high-speed jet that penetrates the gaps. The intermolecular forces between exposed aluminosilicate fibers are extremely weak and cannot resist the surface shear forces generated by the high-speed fluid. The fluid continuously peels away the microstructure of the fiber surface, leading to structural disintegration of the material and macroscopic pulverization and detachment.

[0036] To overcome the aforementioned hydrodynamic damage, step S1 introduces a high-temperature resistant physical coating isolation. High-temperature resistant physical coating isolation refers to using auxiliary materials with melting points higher than the maximum operating temperature of the annealing furnace and possessing specific mechanical strength to comprehensively seal the fragile flexible porous medium, forcibly altering the contact interface state between the external high-speed fluid and the internal fibers.

[0037] Among the alternative coating materials, high-silica ceramic fiber cloth and pure metal foil are conventional industrial choices. After several high-temperature baking processes, the organic binder inside the ceramic fiber cloth will completely evaporate, causing the cloth itself to become brittle. Under the scouring of airflow, it will not only fail to protect the internal medium, but will also break and peel off. Although pure metal foil can achieve absolute physical isolation, its completely airtight physical property will cause defects during the annealing heating stage. The air trapped inside expands dramatically when heated. Since it cannot escape, it will generate huge expansion compressive stress inside the metal foil, eventually causing the entire coating layer to bulge or even burst and fail.

[0038] This invention preferably uses a high-temperature resistant alloy woven mesh as the material for physical encapsulation and isolation; specifically, it uses 310S austenitic heat-resistant stainless steel wire, which contains a high proportion of chromium and nickel elements. In a high-temperature oxidizing environment, it can form a dense and stable chromium oxide passivation film on the surface of the metal wire, preventing further oxidation of the underlying metal atoms; at the same time, the physical structure of the woven mesh has macroscopic geometric deformation capabilities, which can synchronously adapt to the thermal expansion and contraction of the environment with the internal flexible porous medium.

[0039] This invention uses alloy wires with a diameter of 0.4mm to 0.6mm, woven into a metal mesh with a mesh count of 40 to 60. The porous structure of the metal mesh forms a flow-blocking layer in terms of fluid dynamics. When the high-speed protective gas in the annealing furnace impacts the surface of the metal mesh, the dense metal mesh forcibly cuts the macroscopic high-speed jet into countless tiny fluid bundles. As the fluid bundles pass through the mesh and enter the interior, their kinetic energy is largely consumed through internal fluid friction and viscous dissipation of the mesh wall, causing the fluid velocity penetrating the mesh to decrease and transform into harmless weak turbulence, thus losing the fluid shear force that peels off the internal aluminosilicate fibers. At the same time, the porous structure allows the internal heated and expanded air to seep out smoothly, achieving a dynamic balance of microscopic pressure and avoiding the bursting and deformation of the coating layer.

[0040] Specifically, the aluminum silicate fiber is cut according to the perimeter and height parameters of the target area of ​​the annealed metal protective cover. After the cutting is completed, a uniform pre-compression stress of 0.05MPa to 0.1MPa needs to be applied to the aluminum silicate fiber to cause slight compression of the volume. The purpose of the pre-compression process is to generate elastic potential energy storage in the internal fiber skeleton.

[0041] While maintaining pre-compression, the aluminum silicate fiber blanket is fully wrapped with the prepared 310S high-temperature resistant alloy woven mesh. At the seams of the wrapping, a folding edge-binding process is used to ensure that the overlap width of the mesh layer is not less than 20mm~30mm to prevent the fiber from leaking from the seams under high temperature.

[0042] After the wrapping is completed, the openings and overlapping edges of the woven mesh are mechanically sewn together. The sewing material must be 310S austenitic heat-resistant stainless steel wire, which is exactly the same as the woven mesh material. The purpose of using the same material is to ensure that the sewing thread and the woven mesh body have completely consistent coefficients of linear expansion in high-temperature alternating environments, avoiding tensile breakage of the sewing thread due to differences in thermal expansion displacement. The sewing process requires the stitch spacing to be controlled between 10mm and 15mm, which provides a sufficiently dense mechanical interlocking force to maintain the overall shape of the wrapping layer, while also allowing for a small mesh sliding space between adjacent stitches, giving the entire wrapping layer excellent flexibility and bending adaptability.

[0043] After being processed through the above-mentioned pre-compression, wrapping and high-temperature sewing process, the originally loose and fragile medium is made into a modular flexible thermal insulation core pad.

[0044] After completing the modular coating pretreatment of the flexible porous medium, the physical device assembly and spatial boundary intervention stage begins. During the annealing heating cycle, the significant difference in geometric expansion between the external additional components on the fire-facing side and the original protective cover body on the unfire-facing side due to different heating intensities inevitably leads to high thermal stress concentration and plastic tearing of the interface in traditional continuous rigid constraint assembly. Therefore, while completing the spatial arrangement of the insulation material, it is necessary to break the static deadlock between dissimilar metal components and introduce a dynamic connection architecture that can convert accumulated thermal expansion potential energy into non-destructive sliding displacement to ensure the long-term service stability of the newly added physical structure under extreme thermal shock environments.

[0045] In S2, a flexible heat insulation core pad is assembled in the upper middle part of the metal protective cover to withstand the strong heat radiation of the annealing furnace, so as to construct a local heat barrier buffer zone on the external heat radiation path of the metal protective cover. A discontinuous stress relief connection structure is set between the inner protective cover body and the outer metal liner that constitute the local heat barrier buffer zone.

[0046] Specifically, a flexible thermal insulation core pad is assembled between the inner protective cover body and the outer metal liner as a liner, and is located in the upper-middle region of the inner protective cover body that is subject to heat radiation. After assembly, the liner forms a local thermal barrier buffer zone on the outside of the inner protective cover body. The local thermal barrier buffer zone is formed by the flexible thermal insulation core pad as a liner, and is used to locally block the heat radiation transfer path in the upper-middle region.

[0047] The inner protective cover is a thin-walled metal container used in the annealing process to isolate the open flame combustion atmosphere in the furnace from the cold-rolled steel coil. It is made of high-temperature resistant austenitic stainless steel sheet, rolled and welded together. The external heat radiation path refers to the effective spatial distance that the high-temperature electromagnetic waves generated by the inner wall of the annealing furnace and the jet burner travel to the surface of the inner protective cover.

[0048] Regarding the selection of the assembly location, this invention does not adopt the conventional approach of completely enclosing the entire inner protective cover body, but rather strictly defines the assembly area in the upper-middle region that is subject to heat radiation; the specific parameters of the assembly area are: starting from the horizontal cross-section extending upward from the bottom load-bearing flange of the inner protective cover body at a distance of 1500mm~1800mm, up to the top arc-shaped dome area of ​​the inner protective cover body; in this embodiment, the overall height range of the inner protective cover body is 3000mm~4500mm.

[0049] The upper-middle region was chosen as the location for the local thermal barrier buffer zone because of the physical characteristics of fluid thermal expansion and convective heat transfer. The protective gas in the annealing furnace experiences a rapid decrease in density upon heating, generating a strong upward buoyancy force, causing a large accumulation of high-enthalpy gas in the top space. This accumulation effect, combined with the direct radiation from the jet burner, results in a significantly higher heat flux per unit area in the upper-middle region of the inner protective cover compared to the lower-middle region. While setting an equal insulation layer globally would decrease the overall heating rate, the axial heat input ratio would remain unchanged, and the axial temperature difference in the cold-rolled steel coil would persist. By constructing a local thermal barrier buffer zone only in the upper-middle region, the thermal resistance is artificially increased, forcing the overall heat transfer coefficient in the upper-middle region to increase from the conventional 80 W / m². 2 K~100W / m 2 K decreased to 15W / m 2 K~25W / m 2 K; The targeted application of thermal resistance weakens the heat reaching the upper surface of the cold-rolled steel coil, compensating for the uneven distribution of natural heat caused by gas rising, and laying the foundation for smoothing the axial temperature gradient from the perspective of physical field boundary conditions.

[0050] The outer metal liner is an annular metal shell used to constrain the modular flexible thermal insulation core within a predetermined space. Among the alternative outer metal liner materials, ordinary carbon structural steel undergoes severe oxidation and decarburization in environments exceeding 600°C, forming a loose iron oxide scale on the surface that quickly peels off, failing to provide long-term structural support. While ferritic heat-resistant stainless steel possesses some oxidation resistance, it exhibits a severe tendency for brittle transformation in the 400°C–500°C range, making it highly susceptible to brittle fracture after multiple annealing cycles. Martensitic stainless steel has extremely low creep strength at high temperatures and cannot resist macroscopic deformation caused by its own weight and thermal stress.

[0051] This invention selects 310S austenitic heat-resistant alloy stainless steel, which is the same material as or has a similar coefficient of linear expansion to the inner protective cover body, as the material for the outer metal lining. The 310S austenitic heat-resistant alloy stainless steel contains 24%–26% chromium and 19%–22% nickel by mass. In the oxidizing atmosphere of the annealing furnace at up to 1100°C, the high chromium content can form an extremely thin and dense spinel-type oxide passivation film on the surface of the outer metal lining, blocking the further diffusion of oxygen atoms into the metal lattice.

[0052] The core function of using an austenitic matrix is ​​to maintain the face-centered cubic lattice structure at high temperatures, ensuring that the material possesses excellent high-temperature creep strength and resistance to creep. The thickness of the outer metal liner is 3mm to 5mm. If the thickness is less than 3mm, the liner is prone to local instability and wrinkling at high temperatures due to insufficient stiffness; if the thickness is greater than 5mm, it increases the material's self-weight and intensifies the stress on the high-temperature connection structure.

[0053] In the process of constructing a local thermal barrier buffer zone, the modular flexible thermal insulation core pad prepared in step S1 needs to be assembled into the annular cavity formed between the inner protective cover body and the outer metal liner. The assembly process is not a simple stress-free filling, but requires the application of a specific radial assembly interference. Specifically, the radial geometric gap between the inner protective cover body and the outer metal liner is set to 45mm~50mm, and the initial natural thickness of the filled modular flexible thermal insulation core pad is 55mm~60mm. When the outer metal liner is closed by external mechanical tooling, the flexible thermal insulation core pad is forcibly compressed by 10mm~15mm.

[0054] Therefore, the flexible heat insulation core pad is pressed between the inner protective cover body and the outer metal liner as a pad. Its elastic recovery force makes the pad continuously adhere to the inner and outer metal surfaces, thereby maintaining the spatial position and heat insulation stability of the local heat barrier buffer zone.

[0055] The modular flexible insulation core pad's internal fiber skeleton generates continuous elastic recovery force under pressure, tightly adhering to the metal surfaces of the inner protective cover body and the outer metal liner. This eliminates macroscopic air gaps at the interface, preventing these gaps from becoming bypass channels for annealing furnace gases. The pre-compression state increases the frictional resistance between the metal woven mesh and fibers inside the core pad, overcoming the volumetric settlement and collapse of the insulation material due to its own gravity in the vertical cavity several meters long. This maintains the consistency of the thermal resistance coefficient of the local thermal barrier buffer zone along the height direction.

[0056] After the physical assembly of the sandwich structure is completed, the outer metal liner and the inner protective cover body must be mechanically connected; the existing technology generally adopts a process of continuous full welding along the edge of the outer metal liner for rigid fixation.

[0057] Because the inner surface of the inner protective cover is in contact with the relatively low-temperature cold-rolled steel coil and circulating cooling gas, while the outer surface of the outer metal lining is directly exposed to the ultra-high temperature radiation of the annealing furnace; during the heating stage, the heating rate and absolute temperature of the outer metal lining are always higher than those of the inner protective cover, forming a radial temperature gradient of up to 150℃~250℃ between the two; the linear expansion coefficient of austenitic stainless steel is approximately 16×10⁻⁶. -6 At a temperature of / ℃, over a height span of 3000mm, the temperature difference will cause the outer metal liner to elongate by 10mm~15mm more than the inner protective cover body. Because the continuous full weld restricts macroscopic displacement, and the yield strength of the austenitic stainless steel decreases significantly above 900℃, all the locked expansion displacement is converted into internal compressive and shear stresses. Internal stresses exceeding the material's yield limit force the outer metal liner to bulge and buckle, ultimately tearing the weld from the fragile heat-affected zone at the grain boundaries.

[0058] To overcome the thermal shock structural failure caused by the rigid constraints mentioned above, S2 is equipped with a discontinuous stress relief connection structure. The discontinuous stress relief connection structure abandons the continuous closed welding logic and introduces a discretized mechanical bridging and geometric slip mechanism. Specifically, a rectangular metal bridging block with a cross-sectional size of 50mm×10mm is used as the transition connection medium between the inner and outer boundaries. A metal bridging block is arranged at an arc length interval of 200mm~300mm along the lower edge circumference of the outer metal liner.

[0059] For the fixing of each metal bridging block, an asymmetric welding constraint strategy is adopted. The end of the metal bridging block near the inner protective cover body is permanently and rigidly fixed with a full-penetration fillet weld, making it a cantilever support node on the inner protective cover body; the end of the metal bridging block near the outer metal liner is connected by a guide groove; an axially elongated groove with a length of 25mm~30mm is pre-machined at the corresponding position on the outer metal liner, and a fastening pin with a large washer is used to connect the outer metal liner to the metal bridging block through the groove; the torque of the fastening pin is precisely controlled to ensure that a small axial sliding clearance of 0.5mm~1.0mm is maintained between the washer and the surface of the outer metal liner.

[0060] When the local thermal barrier buffer zone enters the rapid heating stage with the annealing furnace, the outer metal lining undergoes violent outward and upward expansion due to the absorption of a large amount of thermal radiation. Because of the sliding clearance, the metal body of the outer metal lining can slide freely upward along the trajectory of the axial elongated groove, converting the accumulated thermal expansion potential energy into non-destructive relative mechanical displacement. At this time, the metal bridging block only undertakes the radial support and gravity bearing function of the outer metal lining, without restricting its axial deformation. This displacement release mechanism avoids the exponential accumulation of internal stress in the material, ensuring that the outer metal lining does not bulge or buckle when experiencing severe temperature fluctuations, thus maintaining the overall macroscopic structural integrity of the device.

[0061] Due to the use of a discontinuous stress-relief connection structure, an unsealed structural gap exists between the outer metal liner and the inner protective cover body. This geometric gap, which allows for thermal expansion and slippage, constitutes a channel for the intrusion of high-speed protective gas within the annealing furnace from a hydrodynamic perspective. When convective gas with an external velocity of 15 m / s encounters the structural gap, the airflow velocity at the gap inlet will further surge due to the streamline contraction effect, forming a jet with strong cutting kinetic energy that directly impacts the internal modular flexible heat insulation core pad. Although the outer layer of the core pad has a high-temperature resistant metal woven mesh, long-term local high-speed jets can still cause fatigue fracture of the metal mesh wires, leading to the pulverization and loss of internal fibers.

[0062] To cut off the direct hydrodynamic scouring path, a metal flow-blocking baffle is added inside the connection gap, behind the windward flow channel, while setting a discontinuous stress-relieving connection structure. The flow-blocking baffle is a 2mm thick annular metal bending piece. During assembly, the root of the flow-blocking baffle is continuously and fully welded to the outer wall of the inner protective cover body. The blocking surface of the baffle is perpendicular to the direction of the possible incoming airflow, and a dynamic clearance gap of 2mm to 3mm is reserved between the outer edge of the baffle and the inner wall of the outer metal liner.

[0063] The flow baffle is used to block high-speed protective gas from directly impacting the flexible heat insulation core pad as a liner through the connection gap, so as to prevent the outer covering structure and the internal flexible porous medium of the liner from being damaged or pulverized by continuous fluid scouring.

[0064] The working principle of adding a flow-blocking baffle lies in the forced dissipation and directional induction of fluid dynamic pressure. When a high-speed external jet enters through the structural gap, the fluid first impacts the surface of the flow-blocking baffle in the forward direction. The physical obstruction causes the fluid velocity to approach zero instantaneously, and the dynamic pressure is rapidly converted into static pressure, forming a stagnation zone in fluid mechanics. The gas that has lost its initial kinetic energy can only overflow into the depth of the annular chamber through the 2mm~3mm dynamic clearance gap reserved at the edge. After the dual attenuation of stagnation dissipation and gap throttling, the gas velocity reaching the surface of the modular flexible heat insulation core pad is reduced to a low-speed vortex state of less than 1m / s.

[0065] Low-speed gas does not possess the shear kinetic energy to destroy the metal woven mesh and fiber skeleton, and its slow permeation characteristic can balance the gas pressure inside the annular chamber; the reserved dynamic clearance not only meets the fluid throttling function, but also avoids rigid physical interference between the outer metal lining and the flow-blocking baffle during the thermal expansion sliding process, thus taking into account the movement space requirements of the stress release mechanism.

[0066] After completing the physical boundary assembly of the local thermal barrier buffer zone and the construction of the discontinuous stress relief connection structure, the device transitions from a static to a dynamic heat treatment process. By initiating a predetermined annealing heating procedure, the pre-deployed metal and thermal insulation composite entity is prompted to intervene in the heat transfer path in the high-temperature field, transforming the originally localized unbalanced thermal radiation into uniform and controllable heating boundary conditions.

[0067] In step S3, the inner protective cover body equipped with a local thermal barrier buffer belt and the cold-rolled steel coil inside it are annealed and heated. When the furnace ambient temperature enters the core heating range, the local thermal barrier buffer belt is used to block the direct thermal radiation from the heat source of the annealing furnace to the upper part of the inner protective cover body, thereby reducing the difference in thermal conduction rate between the two ends of the cold-rolled steel coil in the axial direction.

[0068] Annealing heating refers to a systematic process in which the annealing furnace control system continuously inputs heat energy into the furnace by adjusting the fuel supply and combustion air volume according to a pre-set time-temperature relationship curve, thereby causing the heated object to undergo internal metal lattice reconstruction and residual stress elimination.

[0069] The heat source of an annealing furnace is usually composed of multiple high-speed jet burner arrays arranged tangentially along the inner circumference of the furnace wall. The burners generate high-speed, high-temperature flame jets and high-temperature furnace gas by mixing and burning natural gas and air. After the inner wall of the furnace is heated by the flame, it, together with the high-temperature furnace gas itself, emits heat radiation and convective heat transfer into the furnace, forming the basis for the external heat energy supply of the annealing process.

[0070] The core heating range of annealing refers to the temperature span between the critical point where the residual stress inside the material begins to be released in large quantities during the annealing cycle of cold-rolled steel coils and the highest holding temperature at which the metal grains undergo complete recrystallization. The core heating range is defined as an ambient temperature of 400℃ to 1000℃. The difference in heat conduction rate refers to the numerical difference in the amount of heat transferred per unit area of ​​surface area to the interior of the cold-rolled steel coil between the upper and lower end surfaces at the same moment. The physical dimension is expressed as the difference in heat flux density, reflecting the asymmetry of the heating state of the cold-rolled steel coil along the height direction.

[0071] The inner protective cover, containing the cold-rolled steel coil and equipped with a localized thermal barrier buffer, is hoisted onto the annealing furnace base, and the bottom mechanical seal is completed. A protective gas mixture of pure hydrogen or hydrogen-nitrogen is introduced into the inner protective cover, and the bottom circulating fan is started. The annealing furnace heat source is ignited and begins the initial convective heating stage. In the initial heating phase from room temperature to 400℃, the power output of the annealing furnace heat source is relatively low, and heat transfer within the furnace is primarily through convective heat exchange of the high-temperature furnace gas. At this time, due to the low overall temperature baseline, the intensity of thermal radiation is relatively weak, and the difference in heat received by the upper and lower ends of the cold-rolled steel coil is within the range that the material's own thermal conductivity can compensate for, resulting in a relatively uniform temperature field inside the cold-rolled steel coil.

[0072] As the annealing heating progresses, when the furnace ambient temperature exceeds 400℃ and continues to climb towards 1000℃, officially entering the core heating range of annealing, the thermodynamic heat transfer mechanism within the annealing furnace changes. According to Stefan Boltzmann's law of thermal radiation, the thermal radiation energy emitted by an object is proportional to the fourth power of its thermodynamic temperature. Within the high-temperature range, the intensity of thermal radiation emitted by the heat source of the annealing furnace increases exponentially, and thermal radiation rapidly replaces convection heat transfer, becoming the dominant heat transfer mode within the furnace, accounting for over 80% of the total heat transfer.

[0073] Due to the natural upward accumulation effect caused by the reduced density of the high-temperature furnace gas, coupled with the unobstructed direct radiation from the annealing furnace heat source to the upper and middle spaces, the upper part of the inner protective cover receives a high density of thermal radiation flux. The cold-rolled steel coil is an anisotropic heat transfer body made of thousands of layers of extremely thin metal strips tightly wound together. In the radial direction, there are microscopic gas gaps and contact thermal resistance between the layers, resulting in extremely low radial equivalent thermal conductivity of the steel coil, which is only 5% to 10% of the axial thermal conductivity. External heat is difficult to penetrate radially into the interior of the steel coil, and most of the heat is conducted axially into the interior through the exposed upper and lower surfaces of the steel coil.

[0074] When the conventional process enters the core heating zone of annealing, the high-temperature inner wall of the upper part of the inner protective cover transfers a large amount of heat radiation to the upper surface of the cold-rolled steel coil. However, the lower surface of the cold-rolled steel coil, being in the physical shadow zone and close to the heat-absorbing base, receives less heat flux. The significant asymmetry of the external thermal boundary conditions leads to an increased heat conduction rate on the upper surface of the cold-rolled steel coil, while the heat conduction rate on the lower surface remains at a low level. This difference in heat conduction rate creates a steep temperature gradient along the axial direction inside the steel coil. The upper strip heats up rapidly and generates a large radial thermal expansion displacement, while the lower strip has a lower temperature and a small expansion. The different radial expansion at the upper and lower ends translates into large interlayer tangential shear stresses in the strip layers. When the shear stress exceeds the yield strength of the steel at the corresponding temperature, macroscopic interlayer relative slippage occurs between adjacent strips. Friction and misalignment form penetrating mechanical scratches and plastic deformations on the strip surface, resulting in the strip-shaped indentation quality defect commonly found in the industry.

[0075] The physical device intervened in the aforementioned unfavorable heat transfer process through pre-assembly. When the furnace ambient temperature entered the core heating range of 400℃~1000℃ for annealing, the high-intensity thermal radiation emitted by the annealing furnace heat source impacted the outer metal lining surface covering the upper part of the inner protective cover body. After absorbing heat, the outer metal lining rapidly increased in temperature, but the modular flexible heat insulation core pad on its back functioned as a barrier. The densely interwoven aluminosilicate fiber network and tiny air chambers inside the modular flexible heat insulation core pad together formed a high-resistance thermodynamic barrier. Since the equivalent thermal conductivity of the material remained at a low level at high temperatures, a large amount of heat conducted from the outer metal lining to the fiber layer was retained and reflected.

[0076] The intervention of the local thermal barrier buffer zone creates a large temperature drop zone in the upper middle part of the inner protective cover body; it blocks the direct thermal radiation penetration of the annealing furnace heat source to the upper part of the inner protective cover body, thereby reducing the temperature rise curve of the inner surface of the upper part of the inner protective cover body; as the external heat input of the upper end face is physically throttled, the driving force for heat transfer to the inside of the steel coil decreases accordingly, and the heat conduction rate of the upper end face is suppressed.

[0077] Meanwhile, the heat source at the bottom of the annealing furnace continues to output heat to the lower part of the unshielded inner protective cover body; due to the blockage of the heat at the top, the high-temperature furnace gas circulating in the annealing furnace carries more residual heat and flows downward, increasing the convective heat transfer intensity in the lower part of the inner protective cover body; the lower part of the inner protective cover body transfers heat to the internally circulating protective gas, and the protective gas then continuously transports heat to the lower end face and lower outer surface of the cold-rolled steel coil.

[0078] The spatial heat flow redirection mechanism based on physical impedance achieves the process goal of reducing the difference in heat conduction rate between the upper and lower ends of the cold-rolled steel coil along the axial direction. The upper end of the cold-rolled steel coil is in a state of slow heating with limited flow, which provides a certain time window for heat accumulation and temperature rise at the lower end. The heating curve of the lower end gradually catches up with and approaches the heating curve of the upper end. Through thermodynamic control, the originally steep internal temperature gradient of the cold-rolled steel coil is smoothed out, and the temperature field distributed along the axial height tends to be uniform.

[0079] When the heating rates at both ends of the steel coil are kept synchronized, the volume expansion caused by the metal lattice absorbing heat energy is uniform across the entire height of the steel coil; the radial thermal expansion displacement difference between each layer of strip is limited to a safe threshold, avoiding the generation of destructive tangential shear stress that induces interlayer slip; under stable and synchronized thermal expansion conditions, each layer of strip completes the recrystallization process of the internal grains.

[0080] In step S3, while performing thermodynamic intervention to smooth the internal temperature gradient of the cold-rolled steel coil, the ambient temperature inside the annealing furnace continues to rise towards the highest target value. The outer metal liner directly bears high-intensity radiation, while the inner protective cover body is shielded by the outer metal liner, resulting in differential thermal expansion between the outer metal liner and the inner protective cover body. To prevent the accumulated thermal stress from causing buckling and tearing of the local thermal barrier buffer zone, the discontinuous stress relief connection structure preset during the assembly stage plays a dynamic mechanical guiding role, converting the expansion potential energy into displacement and maintaining the long-term stability of the thermodynamic intervention device.

[0081] In step S4, as the ambient temperature continues to rise, the differential thermal expansion displacement between the inner protective cover body and the outer metal liner caused by temperature changes is absorbed through the discontinuous stress relief connection structure, thereby completing the annealing process.

[0082] The continuous rise in ambient temperature indicates that the power output and radiation intensity of the annealing furnace heat source reach their design limits. The high-temperature gas circulating rapidly along the furnace wall projects heat energy into the space where the inner protective cover is located. The outer metal lining, as the outermost physical boundary of the local thermal barrier buffer zone, is directly exposed to a high thermal radiation flux. According to the physical laws of heat conduction and radiation, after the metal surface of the outer metal lining absorbs radiation energy, its thermodynamic temperature rises sharply and approaches the macroscopic ambient temperature inside the annealing furnace. The inner protective cover is under the double shielding of the outer metal lining and the modular flexible thermal insulation core pad.

[0083] The modular flexible thermal insulation core pad utilizes its low equivalent thermal conductivity to block most of the direct penetration of heat radiation, reducing the heat flux transferred to the outer surface of the inner protective cover. At the same time, the inner surface of the inner protective cover continuously exchanges heat with the lower-temperature internal circulating protective gas and cold-rolled steel coil through convection and radiation, acting as a cooling boundary for heat dissipation inward. The spatial heat transfer structure and heat source distribution form a continuous and steep temperature gradient on the radial cross-section of the local thermal barrier buffer zone. The temperature of the outer metal lining is higher than that of the inner protective cover, and the radial temperature difference between the two is maintained in the range of 150℃ to 250℃.

[0084] The asymmetric distribution of the temperature field triggers the volume expansion effect of metallic materials. Both the inner protective shield body and the outer metallic lining are made of austenitic heat-resistant stainless steel, with a linear expansion coefficient of 16 × 10⁻⁶ within the high-temperature range of 800℃ to 1100℃. -6 / ℃~18×10 -6 / ℃. The thermal expansion of a material is the product of its linear expansion coefficient, initial geometric dimensions, and absolute temperature rise. The inner protective cover and the outer metal liner have an axial height span of 3000mm~4000mm in the annealing equipment, amplifying the aforementioned temperature difference of 150℃~250℃ on a macroscopic geometric scale. Through solid mechanics calculations, the absolute elongation of the outer metal liner in the axial direction exceeds that of the inner protective cover by 10mm~15mm; radially, the outer metal liner also undergoes outward expansion. The difference in geometric deformation caused by the inconsistent temperature field is the differential thermal expansion displacement. The expansion potential energy accumulated by this differential thermal expansion displacement is substantial and cannot be eliminated by changing the heating rate or adjusting the gas flow rate.

[0085] In systems without discontinuous stress-relieving connection structures, the inner and outer metal boundaries are designed as continuous, fully welded, rigid connections. When differential thermal expansion displacement occurs under rigid constraints, the mechanical response manifests as an increase in internal stress. The tendency of the outer metal liner to extend freely along the axial and radial directions is locked by the continuous weld to the inner protective cover body, which has a smaller expansion. The suppressed geometric displacement is converted into thermal stress within the metal lattice according to Hooke's law. The outer metal liner body bears bidirectional compressive stress, while the weld and heat-affected zone, serving as connection nodes, bear tangential shear stress. When the ambient temperature exceeds 900℃, the grain boundary sliding of austenitic stainless steel intensifies, and the high-temperature yield strength drops below 30MPa. The continuously accumulated thermal stress breaks through the material's high-temperature yield limit. Under conditions where stress relief mechanisms are lacking, the thin metal plate of the outer metal liner undergoes irreversible plastic instability, manifesting as bulging and wrinkling deformation. When deformation intensifies, the shear stress concentrated at the weld tears apart the coarse-grained heat-affected zone, causing large-area structural fracture at the connection. The weld seam tears and damages the physical shell of the local thermal barrier buffer zone, causing the internal insulation medium to be directly exposed to the high-temperature and high-speed furnace gas with a flow rate of 15m / s to 20m / s. This leads to the oxidation and pulverization of the insulation material and its loss, resulting in the failure of the thermodynamic intervention device.

[0086] The discontinuous stress-relieving connection structure deployed in the early assembly stage severs the mechanical transmission chain between thermal stress accumulation and structural failure at the physical boundary. As the ambient temperature continues to rise, differential thermal expansion displacement drives geometric deformation of the outer metal liner, transforming the working mode of the discontinuous stress-relieving connection structure from static rigid support to dynamic mechanical sliding. Metal bridging blocks welded to the inner protective cover body act as mechanical anchor points, maintaining a relatively static spatial position. After absorbing heat, the outer metal liner, relying on pre-machined axial elongated grooves, shifts relative to the metal bridging blocks and the inner protective cover body. Fastening pins penetrating the grooves radially restrict the outer metal liner from detaching from its original layer, while axially granting it freedom of movement. A pre-set micro-gap of 0.5mm~1.0mm between the fastening pin washer and the outer metal liner surface reduces the static friction coefficient between the metal surfaces, ensuring that sliding at high temperatures will not result in mechanical jamming.

[0087] The 10mm~15mm axial expansion of the outer metal liner due to heating is converted into displacement along the groove trajectory. This displacement dissipates the expansion potential energy that would otherwise be converted into internal destructive stress, preventing compressive and shear stresses exceeding the material's high-temperature yield limit from forming on the outer metal liner body and at the connection nodes. During temperature rise, the outer metal liner maintains the flatness and macroscopic geometric stability of the plate, preventing bulging instability and weld tearing.

[0088] By absorbing differential thermal expansion displacement to prevent physical shell rupture, the discontinuous stress-relieving connection structure maintains the structural integrity of the local thermal barrier buffer zone; the outer metal liner structure remains intact, isolating the protective gas circulating at high speed within the annealing furnace outside the annular chamber; the modular flexible insulation core pad exists in a relatively static and pressure-balanced physical space, avoiding physical stripping by fluid shear forces and chemical oxidation by the high-temperature oxygen-containing atmosphere. The microfiber skeleton of the modular flexible insulation core pad remains intact, and its internal micro-air gaps and set volumetric density parameters remain constant. The stable physical state of the modular flexible insulation core pad ensures that the macroscopic thermal resistance coefficient of the local thermal barrier buffer zone does not decrease with prolonged heating time, allowing the device to continuously block local thermal radiation during the high-temperature insulation stage.

[0089] The temperature alternation in the annealing process also includes the controlled cooling stage in the later stages of the annealing procedure. During the cooling process, the external heat source stops inputting energy, and the ambient temperature inside the annealing furnace drops rapidly. The outer metal lining radiates heat outward, and its cooling rate is faster than that of the shielded inner protective cover body. The physical behavior of the material reverses, and the outer metal lining undergoes a linear shrinkage displacement that contracts inward. The discontinuous stress-relieving connection structure has bidirectional mechanical adaptability. The outer metal lining slides in the opposite direction along the slide track, compensating for the reduction in geometric dimensions caused by shrinkage. The bidirectional displacement absorption mechanism prevents tensile stress concentration at the connection nodes during the cooling stage, avoids thermal fatigue cracks caused by alternating hot and cold cycles, and improves the structural reliability of the local thermal barrier buffer zone against multiple rounds of thermal shock.

[0090] Maintaining the structural integrity of the local thermal barrier buffer zone provides physical assurance for the strategy of mitigating temperature gradients throughout the entire annealing cycle. The local thermal barrier buffer zone maintains stable high thermal resistance characteristics, continuously and steadily reducing the heat radiation flux received by the upper surface of the cold-rolled steel coil within the core heating zone and high-temperature holding zone. This continuous blockage of the heat flow channels keeps the difference in heat conduction rate between the upper and lower ends of the cold-rolled steel coil at an extremely low level over a long period, allowing sufficient time for heat accumulation on the lower surface of the coil, and establishing a uniform temperature field along the entire axial direction within the coil.

[0091] Example 1: A method for reducing axial temperature difference during steel coil annealing using a gasket, comprising the following steps: Alumina silicate fiber blanket with a bulk density of 112 kg / m3 was selected as a flexible porous medium. After being cut to a predetermined size, a uniform pre-compression stress of 0.075 MPa was applied to compress its volume. Under the pre-compression state, a 310S type austenitic heat-resistant stainless steel alloy woven mesh with a wire diameter of 0.5 mm and a mesh count of 50 was used to wrap the alumina silicate fiber blanket in all directions. The seams were folded and bound with an overlap width of 25 mm, and mechanically sewn with stainless steel wire of the same material at a stitch spacing of 12 mm to make a modular flexible heat insulation core pad.

[0092] The radial geometric gap between the inner protective cover body and the outer metal liner is set to 48mm. The flexible heat insulation core pad prepared above is filled into this gap and mechanical tooling is applied to close it. Metal bridging blocks are discretely arranged around the lower edge of the outer metal liner. One end of the metal bridging block is fully welded to the inner protective cover body, and the other end is connected by a fastening pin passing through the axial long strip groove of the outer metal liner. An axial sliding clearance of 0.75mm is maintained between the fastening pin washer and the surface of the outer metal liner to complete the assembly.

[0093] Example 2: A method for reducing axial temperature difference during steel coil annealing using a liner. Similarities to Example 1 will not be repeated here, except that the selected aluminosilicate fiber blanket has a bulk density of 96 kg / m³. 3 .

[0094] Example 3: A method for reducing axial temperature difference during steel coil annealing using a liner. Similarities to Example 1 will not be repeated here, except that the selected aluminosilicate fiber blanket has a bulk density of 128 kg / m³. 3 .

[0095] Example 4: A method for reducing axial temperature difference during steel coil annealing using a gasket. The similarities to Example 1 will not be repeated here. The difference is that the axial sliding clearance between the fastening pin washer and the outer metal liner surface is 0.5 mm.

[0096] Example 5: A method for reducing axial temperature difference during steel coil annealing using a gasket. The similarities to Example 1 will not be repeated here. The difference is that the axial sliding clearance between the fastening pin washer and the outer metal liner surface is 1.0 mm.

[0097] Example 6: A method for reducing axial temperature difference during steel coil annealing using a liner. The similarities with Example 1 will not be repeated here. The difference is that the austenitic heat-resistant stainless steel alloy woven mesh selected has a mesh count of 40.

[0098] Example 7: A method for reducing axial temperature difference during steel coil annealing using a gasket. The similarities with Example 1 will not be repeated here. The difference is that the austenitic heat-resistant stainless steel alloy woven mesh selected has a mesh count of 60.

[0099] Example 8: A method for reducing axial temperature difference during steel coil annealing using a gasket. Similarities to Example 1 will not be repeated here, except that the bulk density is 96 kg / m³. 3 Use with 60-mesh woven netting.

[0100] Example 9: A method for reducing axial temperature difference during steel coil annealing using a gasket. The similarities to Example 1 will not be repeated, except that the bulk density is 128 kg / m³. 3 Use with 40-mesh woven netting.

[0101] Comparative Example 1: A method for reducing axial temperature difference during steel coil annealing using a liner. Similarities to Example 1 will not be repeated here, except that the selected aluminosilicate fiber blanket has a bulk density of 60 kg / m³. 3 .

[0102] Comparative Example 2: A method for reducing axial temperature difference during steel coil annealing using a liner. Similarities to Example 1 will not be repeated here, except that the selected aluminosilicate fiber blanket has a bulk density of 160 kg / m³. 3 .

[0103] Comparative Example 3: A method for reducing axial temperature difference during steel coil annealing using a gasket. The similarities to Example 1 will not be repeated here. The difference is that the two ends of the metal bridging block are continuously and fully welded to the inner protective cover body and the outer metal liner, respectively, and the axial sliding clearance is 0mm.

[0104] Comparative Example 4: A method for reducing axial temperature difference during steel coil annealing using a liner. The similarities to Example 1 will not be repeated here. The difference is that rock wool fiber blanket is used instead of aluminum silicate fiber blanket as a flexible porous medium.

[0105] Comparative Example 5: A method for reducing axial temperature difference during steel coil annealing using a liner. The similarities to Example 1 will not be repeated here. The difference is that the aluminum silicate fiber blanket is not wrapped with an alloy woven mesh, but is directly exposed and filled into the radial geometric gap.

[0106] Experimental Example 1: Examples 1 to 7 and Comparative Examples 1 to 5 were selected to conduct simulated annealing tests on the obtained composite thermal insulation devices to obtain the dynamic equivalent thermal conductivity at 1000℃, the peak value of the maximum interfacial shear stress, and the fiber mass loss rate after thermal shock cycling.

[0107] The dynamic equivalent thermal conductivity at 1000℃ was determined using a high-temperature protective hot plate method under simulated conditions of 15 m / s protective gas passing over the surface. The peak value of the maximum interfacial shear stress was obtained by attaching high-temperature resistant strain gauges to the metal bridging block joints and collecting strain data in real time during a rapid temperature rise from room temperature to 1000℃. The fiber mass loss rate after thermal shock cycling was obtained by precisely weighing and comparing the internal fibers after the device was placed in an alternating environment of 1000℃ and high-speed airflow for five cycles. The test results are shown in Table 1.

[0108] Table 1 Performance test results of composite thermal insulation gaskets under simulated annealing conditions

[0109] Analysis of the experimental data in Table 1 shows that the volumetric density of the flexible porous medium directly regulates its internal heat transfer mode. By confining the microscopic pore size between fibers to near the mean free path of gas molecules, the convective heat transfer path of the gas inside the pores is effectively cut off, and the physical span of solid-phase heat conduction is increased, thus reducing the dynamic equivalent thermal conductivity at high temperatures. When the volumetric density is below the selected range, the radiative heat transfer flux increases because the macroscopic pores inside the medium have a weakened ability to intercept high-temperature thermal radiation. Conversely, when the volumetric density exceeds the selected range, the density of the solid fiber skeleton increases, enhancing the phonon thermal conductivity effect and leading to an increase in the solid thermal conduction rate. Within an appropriate density range, the pore size is compressed to near the mean free path of gas molecules, while the solid-phase network is not excessively continuous, thus simultaneously suppressing convective heat transfer and solid-phase heat conduction, achieving an extremely low dynamic equivalent thermal conductivity.

[0110] Axial sliding clearance reconstructs the mechanical response path of the inner and outer metal boundaries during temperature changes. By providing geometric sliding space, the differential thermal expansion displacement generated by the outer metal liner under heat is guided to the guide groove for release, avoiding destructive shear stress accumulation at the connection interface, ensuring that the interface stress is always kept within the high-temperature yield limit of the material, preventing weld cracking and liner buckling deformation caused by thermal expansion obstruction, and improving the structural reliability of the device under severe temperature change cycles.

[0111] The mesh count of the alloy woven mesh determines the degree of kinetic energy dissipation experienced by the high-speed external airflow before entering the insulation layer. Low-mesh-count meshes have excessively large openings, resulting in insufficient cutting and friction against the high-speed jet. The airflow retains high scouring kinetic energy, directly impacting the internal fibers and causing shearing and structural disintegration on the fiber surface. High-mesh-count, dense metal meshes, on the other hand, forcibly divide the macroscopic jet into countless micro-streams. As the fluid passes through the mesh openings, it experiences intense internal friction and wall viscosity dissipation, significantly reducing its kinetic energy. The airflow reaching the fiber surface loses its destructive shearing ability, effectively preventing fiber mass loss. Fibers lacking a mesh layer are completely exposed to the high-speed airflow, leading to severe structural pulverization even in short cycles.

[0112] The temperature resistance and phase change characteristics of different fiber materials are also crucial. Some alternative materials undergo crystallization shrinkage or structural collapse at high temperatures, and even with the protection of the mesh layer, they cannot maintain volume stability, which also leads to a decrease in thermal insulation function.

[0113] Experimental Example 2: Using the basic parameters from Example 1, an additional bivariate cross-combination example was set up. A high-pressure aerodynamic thermal resistance attenuation test was conducted on the obtained composite insulation device to obtain the aerodynamic thermal resistance attenuation rate parameter. This parameter was obtained by applying a high-temperature airflow of 20 m / s with periodic pressure pulsations to the surface of the device and running it continuously for ten hours, measuring the percentage increase in its thermal conductivity. This parameter reflects the overall structural stability and thermal insulation durability of the material under complex fluid-structure interaction.

[0114] Table 2. Test results of high-pressure aerodynamic thermal resistance attenuation Group <![CDATA[Fiber volume density (kg / m 3 )]]> Mesh count of the woven mesh (mesh) Initial thermal conductivity (W / (m・K)) Thermal conductivity (W / (m・K)) after 10 hours Aerodynamic thermal resistance attenuation rate (%) Example 1 112 50 0.085 0.089 4.7 Example 8 96 60 0.092 0.095 3.2 Example 9 128 40 0.088 0.099 9.5 Table 2 shows that, under long-term alternating aerodynamic loads, there is a synergistic effect between fiber bulk density and mesh count, which together determine the thermal resistance durability of the insulation structure.

[0115] By employing a lower fiber bulk density combined with a higher mesh count, the flexible space of the fiber skeleton absorbs the micro-vibrations generated by periodic pressure pulsations, thus avoiding localized stress concentration. Simultaneously, the high-mesh-count dense metal mesh effectively dissipates the kinetic energy of the external high-speed airflow, ensuring that the internal fiber network maintains its original pore structure and air cell arrangement even under long-term pulsating airflow impact. This parametric coupling allows the initial thermal conductivity to remain essentially constant throughout service life, achieving highly durable thermal resistance performance.

[0116] In contrast, when using a combination of medium density and medium mesh count, the rigidity of the fiber skeleton and its airflow damping effect are both at an intermediate level. Under prolonged aerodynamic loads, some microstructures undergo slight rearrangement and localized densification, resulting in a controlled increase in thermal conductivity. However, when using high fiber bulk density with a low mesh count, the rigid fiber skeleton, due to its dense contact points and strong constraints, struggles to dissipate vibrational energy through minute displacements, leading to localized stress accumulation and potentially causing fiber breakage or compressive yielding.

[0117] Furthermore, the low-mesh-count mesh layer provides insufficient damping for airflow, allowing airflow with scouring kinetic energy to penetrate and reach the fiber surface. The combined effect of the high-density, rigid skeleton and insufficient damping protection causes the fibers to undergo localized collapse, pore closure, and irreversible rearrangement of the microstructure under long-term impact from pulsating airflow. This results in a significant increase in the material's equivalent thermal conductivity over operating time and a marked decrease in thermal resistance.

[0118] Experimental results show that the long-term stability of the thermal insulation structure depends on the degree of matching between the flexibility of the skeleton and the airflow damping. A flexible fiber network with deformability, combined with a high-density mesh layer, can more effectively adapt to alternating aerodynamic loads and avoid cumulative damage to the microstructure. While a high-density skeleton has a low thermal conductivity under static conditions, its long-term thermal resistance stability under dynamic loads is significantly insufficient. This invention achieves a balance between thermal insulation performance and service reliability by precisely defining the matching range between the two.

[0119] Experimental Example 3: In order to further verify the actual industrial effect of the method of reducing axial temperature difference during steel coil annealing using a liner as described in this invention, and the necessity of the evolution of the various technical features of this invention, the inventors conducted multiple rounds of industrial comparative experiments on a Q403 rapid heating annular annealing furnace unit in a steel plant.

[0120] Based on preliminary quality analysis and statistics, a significant positive correlation exists between the occurrence of strip-shaped indentation defects in grain-oriented silicon steel and the heating rate of the annular furnace. In a comparative study of multiple annular furnaces, the Q403 unit had the fastest rotation cycle (only 2.4 hours), resulting in a significantly higher heating rate than conventional units and consequently, the most severe occurrence of strip-shaped indentation defects. Therefore, this experiment aims to improve temperature uniformity during the heating process by constructing a localized thermal barrier buffer zone (insulation lining) and to verify the impact of different connection mechanisms and covering methods on equipment lifespan and long-term quality.

[0121] In the first phase of the experiment, a test inner cover with a local thermal barrier buffer strip was initially designed, and cold-rolled steel coils with specifications of 0.23mm and 0.3mm were selected for the first three rounds of annealing tests.

[0122] Temperature time-series data obtained by embedding thermocouples show that, during the heating process of the same steel coil, the test steel coil with a local thermal barrier buffer zone has a significantly slower heating rate in the core heating range of 400℃ to 1000℃ compared with the steel coil using a conventional inner cover. The temperature uniformity inside the steel coil is significantly improved.

[0123] The surface quality of the steel coils after the first three rounds of annealing was inspected, and the data are shown in Table 3. Table 3. Results of strip indentation testing in the first three rounds of industrial annealing tests

[0124] As can be seen from the table above, the average length of the strip indentation on the cotton-lined test roll is 140m, and the length of the strip indentation on the same roll exceeds 300m. In contrast, during normal production, the length of the 0.23mm strip indentation defect on the Q403 unit is about 380m, and the length of the 0.3mm strip indentation defect is about 290m. It can be seen that cotton lining has a relatively significant effect on improving the strip indentation defect, but has no significant effect on improving the elephant foot defect.

[0125] During rapid heating, heat accumulates excessively in the upper part of the furnace due to the natural rise of gas. The upper surface of a conventional steel coil is forced to withstand a much higher heat flux density than the lower surface, creating a steep temperature gradient that drives interlayer shear stress. The experimental inner casing, by introducing a high thermal resistance medium in the upper and middle regions, artificially weakens the radiative heat transfer coefficient from the inner wall of the casing to the upper surface of the steel coil in this area, thus forcibly flattening the heat input ratio between the upper and lower surfaces at the boundary conditions. As a result, the various layers of strip within the steel coil expand synchronously at similar temperature rise rates, effectively avoiding interlayer micro-misalignment and plastic deformation caused by expansion mismatch, and mechanistically suppressing the formation of strip indentations.

[0126] However, the structural failure problems exposed in Table 3, namely the cracking and detachment of the outer ring weld after only three rounds of testing, precisely confirm the necessity of the stress relief mechanism in this invention. The significant temperature difference between the outer metal lining and the inner protective cover body, under the strong constraint of the continuous weld, converts all the enormous thermal expansion potential energy into interfacial shear stress. When this stress repeatedly exceeds the yield limit of the metallic material at high temperatures, grain boundary slip and the accumulation of plastic strain inevitably lead to fatigue tearing of the weld.

[0127] After three rounds of testing, the weld seam of the outer lining had cracked and fallen off, exposing the inner refractory cotton, which affected its actual performance. Therefore, the manufacturer repaired the two inner covers: one underwent normal welding repair (inner cover number ICSC18-039), and the other had a connector added to the crack (inner cover number ICSC18-040). See Figure 3 .

[0128] Table 4. Industrial annealing test results of inner covers with different repair methods

[0129]

[0130] After repair by the manufacturer, the devices were put into continued testing. One inner cover (ICSC18-039), which underwent normal welding repair, developed top deformation after four rounds of use, and the refractory cotton showed severe powdering. Another inner cover (ICSC18-040) showed no obvious external deformation, but the refractory cotton also showed some oxidation. Figure 4 , Figure 5 Experimental results show that constructing a local thermal barrier buffer zone effectively shortens the cumulative length of strip indentations on the surface of the steel coil.

[0131] The inner cover repaired using normal welding essentially repeated the original rigid constraint error, and its mechanical boundary conditions remained unchanged. Therefore, after four uses, macroscopic deformation at the top and severe pulverization of the refractory cotton occurred. This was due to stress concentration in the weld area causing further damage, which in turn triggered a chain reaction where the internal medium was mechanically eroded by high-speed airflow and destroyed by high-temperature oxidation. Conversely, a repair solution that introduces a bridging connector at the crack provides displacement space for the thermal expansion of both internal and external components.

[0132] Although the optimal design could not be formed due to limitations in repair conditions, the fact that the exterior remained without significant deformation and the internal cotton layer only underwent controlled oxidation strongly proves the correctness of the core strategy of converting thermal expansion potential energy into harmless sliding displacement. This severs the transmission chain between stress accumulation and structural disintegration at the root of solid mechanics, protects the integrity of the physical shell, and thus protects the thermal insulation medium from hydrodynamic erosion, ultimately maintaining long-term stable thermal resistance performance.

[0133] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for reducing axial temperature difference during steel coil annealing using a gasket, characterized in that, include: S1. High-temperature resistant physical coating and isolation are applied to flexible porous media to create modular flexible heat insulation core pads; S2. The flexible heat insulation core pad is assembled on the upper middle part of the outer side of the inner protective cover body to withstand heat radiation, forming a local heat barrier buffer zone. A discontinuous stress relief connection structure is constructed between the inner protective cover body and the outer metal liner of the local heat barrier buffer zone. The inner protective cover body and the outer metal liner together constitute the metal protective cover. S3. Annealing and heating the metal protective cover equipped with a local thermal barrier buffer zone and the cold-rolled steel coil inside it. When the ambient temperature inside the furnace enters the core heating range, the local thermal barrier buffer zone is used to block the direct thermal radiation from the heat source of the annealing furnace to the upper part of the inner protective cover body, thereby reducing the difference in thermal conduction rate between the two ends of the cold-rolled steel coil in the axial direction. S4. During the high-temperature annealing process, a discontinuous stress-relieving connection structure is used to absorb the differential thermal expansion displacement between the inner protective cover body and the outer metal liner caused by temperature changes, so as to complete the annealing process. The modular flexible heat insulation core pad is a liner used to reduce the axial temperature difference during the annealing process of steel coils. The liner is composed of a flexible porous medium that is physically coated and isolated by high temperature resistance, and forms the local heat barrier buffer zone by being assembled on the upper middle part of the outer side of the inner protective cover body to withstand heat radiation.

2. The method for reducing axial temperature difference during steel coil annealing using a gasket according to claim 1, characterized in that: In step S2, the discontinuous stress relief connection structure uses discretely arranged metal bridging blocks as the transition connection medium between the inner and outer boundaries. One end of the metal bridging block is rigidly fixed to the inner protective cover body, and the other end is connected to the outer metal liner through a guide groove with sliding clearance, allowing the outer metal liner to slide freely along the axial direction to release thermal expansion potential energy.

3. The method for reducing axial temperature difference during steel coil annealing using a gasket according to claim 1, characterized in that: In step S2, the local thermal barrier buffer strip is only installed in the upper middle region of the inner protective cover body. The upper middle region is defined as the horizontal cross-section extending upward from the bottom load-bearing flange of the inner protective cover body at a distance of 1500mm~1800mm to the top arc-shaped dome region of the inner protective cover body. It is used to target and weaken the thermal radiation in this region and compensate for the uneven natural distribution of heat in the furnace. The local thermal barrier buffer strip is formed by the flexible heat insulation core pad as a liner.

4. The method for reducing axial temperature difference during steel coil annealing using a gasket according to claim 1, characterized in that: In step S1, the high-temperature resistant physical coating and isolation uses a high-temperature resistant alloy woven mesh to wrap the flexible porous medium. The seams of the wrapping are made using a folded edge wrapping process with an overlap width of 20mm~30mm. After wrapping, the medium is mechanically sewn with metal wire of the same material as the high-temperature resistant alloy woven mesh, with the stitch spacing controlled at 10mm~15mm. The flexible porous medium wrapped by the high-temperature resistant alloy woven mesh constitutes the heat insulation body of the pad.

5. The method for reducing axial temperature difference during steel coil annealing using a gasket according to claim 1, characterized in that: In step S2, a flow-blocking baffle is added inside the connection gap of the discontinuous stress relief connection structure. The root of the flow-blocking baffle is fixed to the outer wall of the inner protective cover body. The baffle blocking surface is perpendicular to the airflow direction and a dynamic clearance gap is reserved between it and the inner wall of the outer metal liner to cut off the direct scouring path of the high-speed protective gas on the flexible heat insulation core pad.

6. The method for reducing axial temperature difference during steel coil annealing using a gasket according to claim 1, characterized in that: In step S1, the flexible porous medium is made of aluminosilicate fiber, with a bulk density controlled at 96 kg / m³. 3 ~128kg / m 3 The thickness is controlled between 40mm and 60mm to establish a gentle temperature gradient attenuation zone in the target area.

7. The method for reducing axial temperature difference during steel coil annealing using a gasket according to claim 1, characterized in that: In step S2, a radial assembly interference is applied during the assembly of the flexible heat insulation core pad. The radial geometric gap between the inner protective cover body and the outer metal liner is smaller than the initial natural thickness of the flexible heat insulation core pad, so that the flexible heat insulation core pad is forcibly compressed to form a continuous elastic restoring force to tightly fit the inner and outer metal surfaces. The flexible heat insulation core pad is pressed between the inner protective cover body and the outer metal liner as a pad.

8. The method for reducing axial temperature difference during steel coil annealing using a gasket according to claim 1, characterized in that: In step S3, the core heating range refers to the temperature range in which the furnace ambient temperature rises from 400℃ to 1000℃. Within this range, heat transfer in the annealing furnace is dominated by thermal radiation. The comprehensive heat transfer coefficient of the upper region of the inner protective cover body is reduced by the local thermal barrier buffer zone, which suppresses the heat conduction rate of the upper end face of the cold-rolled steel coil, provides a time window for heat accumulation on the lower end face, and smooths out the axial temperature gradient inside the cold-rolled steel coil.

9. A method for reducing axial temperature difference during steel coil annealing using a gasket, as described in claim 1, characterized in that: In step S1, after the flexible porous medium is cut, a uniform pre-stress of 0.05MPa~0.1MPa is applied, and then a high-temperature resistant physical coating is applied for isolation.

10. A method for reducing axial temperature difference during steel coil annealing using a gasket, as described in claim 1, characterized in that: The outer metal liner is made of 310S austenitic heat-resistant alloy stainless steel with a thickness of 3mm to 5mm. The liner is composed of a flexible porous medium that has been pre-stressed and then physically coated and isolated at high temperatures.

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